1. The Field of the Invention
The present invention is in the field of composite wall structures and, more specifically, to the field of connectors used to secure together multiple layers of material within the composite wall structures.
2. The Relevant Technology
As new materials and compositions have been continuously developed, novel methods of synergistically combining apparently unrelated materials to form useful composites have also been developed. This is true of the area of building and construction in which high strength structural walls have been fabricated and then coated or layered with highly insulative materials having relatively low strength to provide a structure of both high strength and high insulation. In general, insulation is attached to the structural component. The outer wall structure is first erected. Then, an insulating material is placed on the inside of the outer wall structure, and an inner wall is placed over the insulating material to protect and hide it. The purpose of the insulation layer is to prevent, or at least slow, the transfer of thermal energy between the inner and outer walls.
A commonly used measurement of the thermal insulating qualities of a material is the mathematical coefficient “R” which is a measure of the thermal resistance of a material. The coefficient R is typically equal to the inverse of the coefficient “K” which is a measure of the thermal conductivity of the material. A “high R value” material or device is therefore understood by those in the art as possessing a high thermal resistance or insulating ability.
One of the least expensive and strongest building materials that has found extensive use in the construction industry is concrete, which is formed from a mixture comprising a hydraulic cement binder, water and a relatively low cost and high compressive strength aggregate material, such as rocks, pebbles and sand. Together these form a relatively high strength, low cost building material. Unfortunately, concrete has the drawback of offering poor insulation compared to highly insulating materials such as fiberglass or polymeric foam materials. While an 8 inch slab of concrete has an R value of 0.64, a 1 inch panel of polystyrene has an R value of 5.0. However, these latter materials, while highly insulative, also have the drawback of offering little or no structural strength or integrity.
Although structural walls made of cement or masonry can be fitted and even retrofitted with any number of insulating materials, including insulating mats or foams that are sprayed between an inner and outer wall, the insulation material is not able to impart the most efficient insulation possible due to the required structural bridging of the outer structural wall with the inner structural wall. Such structural bridging is necessary in order for the two-wall structure to have high strength and integrity and to prevent the two walls from collapsing together or separating apart during construction and subsequent use of the building. This has been accomplished through the use of metal studs, bolts, or beams. However, because metal is a very good conductive material (and therefore has very low insulating ability), such studs, bolts, beams, or other means for structurally bridging the two walls together also create a conductive thermal bridge across which heat can readily flow, notwithstanding their being surrounded by ample amounts of insulating material. As a result, heat can rapidly flow from a relatively warm inside wall to a colder outside wall during cold weather, for example. Therefore, although an insulating material may have a relatively high R value, the net R value of the composite wall structure can often be far less due to thermal bridging, thus negating or minimizing the effect of adding additional layers of insulation. Examples of U.S. Patents that disclose a composite wall structure held together using metal tie rods or studs include the following: U.S. Pat. No. 4,393,635 to Long, U.S. Pat. No. 4,329,821 to Long et al., U.S. Pat. No. 2,775,018 to McLaughlin, U.S. Pat. No. 2,645,929 to Jones, and U.S. Pat. No. 2,412,744 to Nelson.
In order to substantially overcome the problems of thermal bridging, some have employed the use of tie rods having a metal portion passing through the concrete layers and a thermally insulating portion passing through the insulating layer (e.g., U.S. Pat. No. 4,545,163 to Asselin). Yet others have developed highly insulative connector rods that are made entirely from high R-value materials in order to connect together the two concrete structural layers while minimizing the thermal bridging effect between the outer concrete layers. For example, U.S. Pat. No. 4,829,733 to Long (hereinafter the “Long '733 Patent)) discloses a plastic connector for forming an insulated wall having inner and outer concrete structural layers with highly insulating layers sandwiched therebetween. Although the plastic connector described in the Long '733 Patent has found some use in the construction industry, the connector described therein can be relatively expensive and difficult to manufacture due to the materials and processes required for forming the connector.
Another problem with the aforementioned connectors is that they do not provide adequate composite action. Composite action, which is well known by those skilled in the art, generally describes how well a multi-layered panel, or composite wall, transfers shear forces between its different layers and is typically identified as a percentage between 0% and 100%. A layered panel having a very high composite action will transfer shear forces very well and will behave like a single laminated panel. Whereas, a layered panel having a very low composite action will not transfer shear forces well and will behave more like a panel having a plurality of disconnected layers. Composite action can provide structural integrity to the wall. Accordingly, it is generally desirable to produce composite walls having high composite action so that they will remain intact when loads are applied to the wall. Existing connectors, however, have thus far proven inadequate for providing composite walls with the desired composite action.
Although Composite Technologies Corporation, the assignee of the Long '733 Patent, has made the claim that some of its connectors are able to provide 40% to 60% composite action, independent testing has shown that such connectors only provide about 10% composite action.
As generally described above, composite walls generally include an insulation layer sandwiched between a structural layer and a fascia layer. The structural layer is typically used as the load-bearing member of the wall. The fascia layer is typically not used to bear a load separated from the structural layer because of insufficient composite action existing between the facia layer and the structural layer. However, if the composite action of the wall was sufficiently high, e.g., between 60% to 100%, the fascia layer could potentially be used to bear a substantial portion of the overall load.
Accordingly, there is currently a need in the art for improved connectors that are simple to manufacture and that can be used to provide insulating composite walls with high composite action.